We investigated the correlation of intraoperative peritoneal lavage smear and gastric wall brushing smear cytology with macroscopic and histologic findings and prognosis, in 216 patients with gastric cancer. Some 196 of these patients underwent gastric resection and 20 did not. The incidence of positive cancer cells determined by these methods was significantly correlated with gastric resection, tumor invasion, and peritoneal dissemination. Among patients without macroscopic peritoneal dissemination, four were found to have positive peritoneal lavage smears or gastric wall brushing smears, respectively. The prognosis of these patients did not differ from that of patients with metastases to the adjacent peritoneum but not the distant peritoneum. These results suggest that peritoneal lavage smears and gastric wall brushing smears are useful for predicting the peritoneal cancer dissemination. Therefore we intend to target patients with no peritoneal metastases (Po) showing positive peritoneal cytology for intensive treatment.